Various structures have been developed in the field of antenna design to maximize signal strength and fidelity while minimizing cost and size. One antenna structure is the tapered slot antenna (TSA). Much of antenna design literature also use “tapered-notch,” “flared-slot,” and “tapered-slot” interchangeably with TSAs. TSAs consist of a tapered slot etched into a thin metal film, either with or without a dielectric substrate on one side of the film.
TSAs are travelling wave type antennas that offer simple, lightweight topology capable of radiating over a wide bandwidth with superior radiation performance and impedance matching compared to other slot antennas. TSAs are frequency independent, meaning the antenna pattern and impedance remain constant over a relatively wide frequency bandwidth. A TSA can be designed with a variety of taper profiles to optimize antenna pattern, bandwidth and/or gain.
One profile has a gradual curve shape with an exponential taper that enables multiple operating frequencies and high gain, is known as an exponential TSA. The exponential TSA is able to operate over wide bandwidths and produce a symmetrical end-fire beam with appreciable gain and low sidelobes. The size of the guiding slot is constant in wavelength and TSAs have a broad operating frequency range, with constant beam width over this range.
FIG. 1 illustrates the basic construction of an Exponentially Tapered Slot Antenna (ETSA) 140. The ETSA 140 comprises a substrate 150, an upper solid copper portion 130, a slot 145, a lower solid copper portion 135, and a radiating element 120. The electrical feed line (not shown) provides an input signal to the radiating element 120. Following the radiating element 120, is a slot 145 with a particular input slot width 115, a slot width at the radiating area 110, and the output slot width 100. The ETSA antenna 140 has two width areas (shown as from 120 to 110, and 110 to 100). The first area (from 120 to 110) being a propagating area to propagate a signal from feed line 120 and the second area 105 defined approximately from slot 145 with width 110 to the output slot 100, guides a travelling wave directionally away from the feed line 120. The ETSA 140 exemplifies the typical TSA comprising three portions: a solid copper upper portion 130, a solid copper lower portion 135, and an input microstrip feed line 120.
The conventional ETSA faces challenges involving beam shaping and beam switching, especially in the context of antenna arrays. Specifically, the topology for wideband application is limited by the technique used to couple the feed line signal to the input slot. The feed line supplying the signal is typically soldered or otherwise electrically connected in a fashion that requires another layer and/or is otherwise not easily removable. Furthermore, to create an array of ETSAs, requires multiple additional layers in the same plane or on different planes such as to require a large amount of additional materials.
The fabrication of conventional TSA antennas carries a high cost of materials for forming a solid curved conductive structure used to radiate the beam. The solid conductive metal on the substrate also creates undesirable surface waves with energy detracting from the radiated signal. Furthermore, the conventional TSA loses energy from the radiated signal to the conductive edges or through absorption into the substrate.
Therefore, a need exists for a compact, cost effective, robust antenna adaptable to operate at multiple frequencies.